KBO encounters Options

[Nafnlaus]

Now that there's a target, does anyone know if there's a plan to search for more bodies along the new route? It occurred to me that James Webb will (hopefully) be launching in late 2018, with 7 times the light collecting area as Hubble. Although they probably have other priorities for it in its early days.

[nprev]

Very much doubt that JWST will play a role anytime soon. The post-launch commissioning process will undoubtedly take several months, and that will be after orbit raising, critical deployments, etc. If the NH team is still thinking of trying for a second target then they'll almost certainly try to book more Hubble & ground-based asset time.

In any case, MU69 is far too small to affect NH's trajectory in any significant way so the encounter timing isn't a major constraint for any follow-on mission. I'd guess that the major limiting factor aside from fuel will be how far out they can go & still be able to use the optical instruments; gonna get nothing but darker out there as the spacecraft recedes from the Sun.

[ZLD]

Seems that the decision to go with the target which required the least amount of propellant would indicate some amount of hope for another flyby.

Maybe NH will discover the KB extends much further than predicted but with a continued decrease in body size and an increase in count. One can hope. Might be interesting when they do a final lookback of an almost edge on Solar System.

[Holder of the Tw...]

Seems that ... some amount of hope for another flyby.

Alan Stern addressed this. The saved fuel is for three purposes. Extra maneuverability as they approach the object, maximize the contact time for an extended mission, and margin for unseen contingencies.

Given the effort required to find the two targets, I think the effort to look for any more is a forlorn hope. Any additional target NH could reach would probably already have shown up in the original search.

I expect that Hubble will be used again a couple of times next year and the year after for two purposes: the most important will be refining the position of 2014 MU69. An incidental side benefit will be making the "detected on four oppositions" threshold necessary for numbering (and naming) the object. But I expect these photos to be limited to a single field of view. We've probably seen the last of the surveys.

[Nafnlaus]

Maybe NH will discover the KB extends much further than predicted but with a continued decrease in body size and an increase in count. One can hope. Might be interesting when they do a final lookback of an almost edge on Solar System.

Of course, eventually you hit the Kupier Cliff and then the odds of finding another target drop off...

[Explorer1]

The new blog post by Emily does confirm that there will be distant observations of other known KBOs in the meantime; the team might as well take advantage of the unique perspective to get some basic lightcurve data on them.

Also slightly related: is a Voyager 1 style family portrait of the planets towards the end of the mission still up in the air? Would our pale blue dot still be resolvable by LORRI at that distance?

[nprev]

NH's instruments aren't capable of finding the edge of the Kuiper Belt, and almost certainly not even capable of discovering new KBOs. They were designed quite specifically for close planetary observations, not for astronomy.

Also, remember, it is exceedingly empty out there. The main asteroid belt is doubtless many orders of magnitude denser.

[Nafnlaus]

It's not *that* sparse, compared to space in general at least. There's believed to be at least 100k KBOs greater than 100km diameter, with over a thousand discovered thusfar. And here even a body 100 meters in diameter would be an excellent find - which, given power law scaling, should be 1000 times more common.

The problem, of course, is finding objects, especially the common small ones, so far away. Hubble certainly isn't going to be spotting really tiny KBOs. But it's not impossible that NH would - 100m from thousands of kilometers away, 1km from tens of thousands, 10km from hundreds of thousands, 100km from millions of kilometers. That said, due to NH's limited optics, it's highly unlikely that it'd have enough advance warning to steer in time if it found something, especially something small. But it still could be interesting just simply from the perspective of making discoveries that wouldn't be possible (or at least highly unlikely) from Earth.

[Herobrine]

But it still could be interesting just simply from the perspective of making discoveries that wouldn't be possible (or at least highly unlikely) from Earth.

That's an interesting idea, but I think the limited bandwidth of the DSN downlink from NH would make it impractical to do the detection (in LORRI data) on Earth. They'd have to make the spacecraft able to process data from LORRI on its own to detect that something unknown (i.e. not a star) can been resolved in the data, and respond to that, either simply by transmitting the data to Earth or by actively trying to acquire additional observations with LORRI and other instruments. I know nothing about how the spacecraft functions at a software level, so I don't know if it would be possible to patch NH to allow it to do that processing and reaction; either way, I'd guess that the team wouldn't be willing to design, test, and deploy (with all of the cost and risks that involves) such a patch unless there were a high probability of finding something of substantial science value. I'd guess the idea (or something similar) was evaluated at some point in NH's history, and that its absence from the mission indicates it was determined to be not feasible or not worthwhile.

[Reed]

That's an interesting idea, but I think the limited bandwidth of the DSN downlink from NH would make it impractical to do the detection (in LORRI data) on Earth. They'd have to make the spacecraft able to process data from LORRI on its own to detect that something unknown (i.e. not a star) can been resolved in the data, and respond to that, either simply by transmitting the data to Earth or by actively trying to acquire additional observations with LORRI and other instruments.

Another complication is that in cruise, NH is spin stabilized at ~5 RPM around the HGA axis. The cameras are perpendicular to the HGA, so they sweep the sky at ~1 deg/s. At this rate, very short exposures would be required to get a usable image. 3 axis pointing consumes propellant (NH has no reaction wheels), so using for long periods in cruise would not be practical.

@Nafnlaus
It is extremely sparse. It may be helpful to think in terms of the average distance between objects. Billions of objects sounds like a lot, but spread over a few thousand cubic AU, the density is pretty low. Space is big. Really big.

[Nafnlaus]

Another complication is that in cruise, NH is spin stabilized at ~5 RPM around the HGA axis. The cameras are perpendicular to the HGA, so they sweep the sky at ~1 deg/s. At this rate, very short exposures would be required to get a usable image. 3 axis pointing consumes propellant (NH has no reaction wheels), so using for long periods in cruise would not be practical.

@Nafnlaus
It is extremely sparse. It may be helpful to think in terms of the average distance between objects. Billions of objects sounds like a lot, but spread over a few thousand cubic AU, the density is pretty low. Space is big. Really big.

And New Horizons will move through another couple dozen AU of it before hitting the Kuiper Cliff - which itself isn't the end of the Kupier belt, just a dropoff in density. There's plenty of superlatives of vastness here that work to cancel each other out to varying degrees. I was just pointing out that the Kuiper belt compares very favorably to the asteroid belt in terms of number of large objects - despite how close the asteroid belt is to us, we already know of five times as many 100km+ KBOs as we know of 100km+ asteroids. It's not some unusually empty space, it's actually pretty heavily populated - as far as space goes.

Good point about spin stabilization, of course - I don't know enough about the details of the system to know whether there's any practical way to make observations while spin stabilized.

[ngunn]

despite how close the asteroid belt is to us, we already know of five times as many 100km+ KBOs as we know of 100km+ asteroids. It's not some unusually empty space

That's five times as many objects in approximately five thousand times the volume. It's pretty empty.

[Alan Stern]

That's five times as many objects in approximately five thousand times the volume. It's pretty empty.

:-) Exactly correct; as I tell public audiences, this is why we call it "space."

[Nafnlaus]

That's five times as many objects in approximately five thousand times the volume. It's pretty empty.

That's five times as many known objects, in an area where objects appear a fraction of a percent as bright as they would in the asteroid belt and present a fraction of a percent as much relative movement to background stars. Not total objects.

We've probably discovered all of the 100km+ asteroids. The last one found was 1902 Shaposhnikov in 1972, and the last one before it was 1390 Abastumani in 1935. We know 100+km asteroids well. The same cannot be said for similar sized KBOs. There's an estimated hundred thousand 100km+ KBOs, all but a thousand or so undiscovered. 500 times as many as in the asteroid belt, not 5.

:-) Exactly correct; as I tell public audiences, this is why we call it "space."

Seriously, don't take my word for it - take the word of one Alan Stern

http://pluto.jhuapl.edu/News-Center/PI-Per...tive_08_24_2012

Since 1992, more than 1,000 KBOs have been discovered. But only a tiny fraction of the sky has been surveyed for KBOs. It is estimated that more than 100,000 KBOs exist with diameters of 100 kilometers or larger, along with billions of smaller objects down to the size of cometary nuclei, just a kilometer or two across.

Sending a probe through the Kuiper belt now is like sending a probe through the asteroid belt in 1803, in terms of the percentage of 100km+ bodies discovered.

NH (if not for the rotation limitations) would be sweeping through a plausible-detection-volume of (very roughly) one cubic AU before hitting the Kuiper Cliff (Alan, correct me if I'm wrong here as to the optical capabilities of NH, I had to make a number of assumptions and ended up with about a 1 million km detection distance** vs. a ~20 AU flight path). Less detection volume for smaller KBOs, but then again, they're much more common. And vice versa for larger KBOs.

As for the odds of an actual discovery, I don't know the distribution of KBOs along the path that NH is taking. The cross section of the Kuiper Belt as viewed from perpendicular to the ecliptic is somewhere on the order of 6000 square AU. Clearly most are going to trend toward the ecliptic but without knowing the exact distribution I have no ability to comment any further on the matter.

** Note: NH was sighting Pluto from 4,2 billion km away. Pluto has 562 times the cross sectional area as a 100km KBO, meaning a "typical" 100km+ KBO could technically be sighted at about 7,4 million kilometers under the same sort of conditions (give or take a wide margin). But then again, it's not a matter of simply sighting a known object in a known position but rather tracking changes over large swaths of sky, and objects get dimmer the further out one goes, so expecting a practical limit nearly an order of magnitude less than that of the September 2006 Pluto sighting seems realistic)

[Nafnlaus]

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